Multilayer plastic films are used for many purposes, for example in the food packaging industry. Such films are described for example in U.S. Pat. No. 6,159,616 (Planeta et al) issued Dec. 12, 2000 and U.S. Pat. No. 6,218,024 (Tamber et al) issued Apr. 17, 2001, the contents of which are hereby incorporated herein by reference.
It is known to irradiate such multi-layer films to improve their properties, for example mechanical properties such as puncture resistance, tensile strength and abuse resistance. However, the problem with irradiating a multi-layer film is that the radiation which improves the properties of one or more layers may adversely affect the properties of another layer or layers. It has been proposed to irradiate a layer before it is bonded with other layers to produce a multi-layer film, but this technique has presented production difficulties.